The case raises a number of ethical questions. For all the promise, researchers have long warned that they must learn to control newly injected stem cells so they don’t grow where they shouldn’t, and small studies in people are only just beginning [AP]. And, because the patient’s immune system was impaired, it’s not yet clear whether the increased risk of cancer is specific to patients with suppressed immune systems, something particular to the procedure done in Moscow, or a danger with neural stem cell transplantation in general, said Uri Tabori, a pediatric hematologist and oncologist…. “It’s a cautionary tale for studies currently being done in the US and elsewhere,” said [Arnold] Kriegstein [The Scientist], a U.S. stem cell researcher.

I have seen similar claims over the years and also claims that non-fetal stem cells don't have this problem. A new discovery has taken a patient's own stem cells and "changed" it into something like a fetal stem cell- a stem cell that can become any other type of cell, without the continued growth with used only on the patient.